Configuring Metro Features
December 2005 © Foundry Networks, Inc. 8 - 7
Ring Initialization
The ring shown in Figure 8.1 shows the port states in a fully initialized ring without any broken links. Figure 8.3
shows the initial state of the ring, when MRP is first enabled on the ring’s switches. All ring interfaces on the
master node and member nodes begin in the Preforwarding state (PF).
Figure 8.3 Metro ring – initial state
MRP uses Ring Health Packets (RHPs) to monitor the health of the ring. An RHP is an MRP protocol packet. The
source address is the MAC address of the master node and the destination MAC address is a protocol address for
MRP. The Master node generates RHPs and sends them on the ring. The state of a ring port depends on the
RHPs.
A ring interface can have one of the following MRP states:
• Preforwarding (PF) – The interface can forward RHPS but cannot forward data. All ring ports being in this
state when you enable MRP.
• Forwarding (F) – The interface can forward data as well as RHPs. An interface changes from Preforwarding
to Forwarding when the port’s preforwarding time expires. This occurs if the port does not receive an RHP
from the Master, or if the forwarding bit in the RHPs received by the port is off. This indicates a break in the
ring. The port heals the ring by changing its state to Forwarding. The preforwarding time is the number of
milliseconds the port will remain in the Preforwarding state before changing to the Forwarding state, even
without receiving an RHP.
• Blocking (B) – The interface cannot forward data. Only the secondary interface on the Master node can be
Blocking.
When MRP is enabled, all ports begin in the Preforwarding state. The primary interface on the Master node,
although it is in the Preforwarding state like the other ports, immediately sends an RHP onto the ring. The
secondary port on the Master node listens for the RHP.
F
PF
F
PF
Switch D
PF
PF
Customer A
PF
F
PF
PF
PF
Switch C
Switch A
Switch B
Master
Node
Customer ACustomer A
Customer A
F
All ports start in
Preforwarding state.
Primary port on Master
node sends RHP 1
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